Vehicles nowadays are armored against projectiles with steel parts (ballistic protection) where to starts with a special type of armor steel is used. Armor steel is slightly alloyed steels of great hardness.
EP 1,052,296 describes by way of example, a steel alloy characterized by a low carbon content and carbon/nitride-forming vanadium. The alloy is formed in mass percentages, namely, out of, by weight
0.15 to 0.2%carbon,0.1 to 0.5%silicon,0.7 to 1.7%manganese,max. 0.02%phosphorus,max. 0.005%sulfur,max. 0.01%nitrogen,0.009 to 0.1%aluminum,0.5 to 1.0%chromium,0.2 to 0.7%molybdenum,1.0 to 2.5%nickel,0.05 to 0.25%vanadium,max. 0.005%boron, andbalance iron including standard impurities.This alloy has a yield point of more than 1100 N/mm2 and a minimum strength of 1250 N/mm2. Its strength-to-break is above 10%. Known ballistic steels are ARMOX 500 T, 560 T and 600 T of SSAB or SECURE 400, 450, 500 and 600 of Thyssen Krupp Stahl.
According to the tempering of the steel, it has either high strength and low ductility, or a sufficient ductility with a lesser hardness. If the steel has to be made into armor plate in particular bent, it is necessary to use relatively expensive bending methods and tools. As a result, standard armored-steel plating is only machined a little for minor changes in dimensions. In particular, it can only be bent up to about 4% without breaking or cracking. As a result of these problems, armor, as a rule, is made up of many small parts that are held together in order to make a complex shape. Welding together the armor-steel parts decreases their hardness greatly in the heated regions. In order to get protection against projectiles for the armor, further armor plates are applied over the welded seams. Alternatively, the welded seams are backed up by an aramide layer. Armor that is not visible from the outside, therefore, takes up considerable inside space. The loss of space can lead to limiting of the functionality of the vehicle when these functions can no longer be built in. An example of this in conventional vehicles is the installation of side and overhead air bags.
German 103 06 063 describes a method of working armor steel. Each workpiece of armor steel is annealed to a temperature above the Curie point for a predetermined time to create an austenitic crystalline structure. Subsequently, the workpiece is cooled at a controlled speed above the critical cooling temperature of martensitic crystalline formation, and the still soft workpiece is shaped. Then the shaped workpiece is brought back to above the Curie point to recreate its hardness. The problem with this method is that reheating and rehardening after shaping creates stress and some deformation in the part. Maintaining exact dimensions is, however, very important for an armored part built into a motor vehicle.
German 24 52 486 describes a method for preshaping and hardening a steel sheet of modest thickness so as to approach accurate dimensioning. Here a plate of boron-alloyed steel is shaped, in less than five seconds, into its final shape between two indirectly cooled tools while being substantially deformed and held in the press while being cooled so quickly that a martensitically or bainetic fine-grained crystalline structure is produced. This method is recommended for extra strong, relatively thin parts and complex shaped and accurate dimensions for structural and safety-related parts, such as A and B-columns or shock absorbers in the civilian motor-vehicle industry. As a result, one of the typical sheets has a thickness of 3 mm or less, and steel with a low carbon content is used. Tests of these steels with respect to the ballistic strength produces a substantially poorer outcome relative to the armor steels available on the market, in particular, it is necessary to use substantially lighter pieces.
German 197 43 802. describes a method of making a metallic-shaped parts for motor vehicles for regions of high ductility. To this end, a plate is prepared of a steel alloy that has as a percentage of weight a content of
0.18% to 0.3%carbon,0.1% to 0.7%silicon,1.0% to 2.5%manganese,max. 0.025%phosphorous,0.1% to 0.8%chromium,0.1% to 0.5%molybdenum,max. 0.01%sulfur,0.02% to 0.05%titanium,0.002% to 0.005%boron,0.01% to 0.06%aluminum, andbalance iron, inc. smelting impurities.This known alloy is particularly good for hot shaping and for armor purposes, however, the wall thickness must be so large that its use is almost ruled out because of weight.
EP 1 335 036 describes a method for making a structural element protected by aluminum against corrosion and produced by piece coating and hot shaping. The goal is to avoid the cool shaping of the aluminum layer.
German 102 08 216 describes a method for producing a partially hardened part where regions of the part are maintained isothermally after austenitizing until the ferrite or perlite is converted and in the subsequent hardening process the regions do not harden into martensite.
German 102 46 164 describes a hot-shaping process for plates made from a flexible rolled strip.
German 103 07 184 describes the prerough and finish shaping of a plate from preheat without intermediate heat.
German 100 49 660 describes the hot shaping of a patchwork plate.
German 197 23 655 describes the hot-shaping method of a steel-plate product where the steel is hardened but kept in fluent condition by parts or recesses of a tool in regions in which it is to be worked afterward.
German 100 16 798 describes armor for a security vehicle where the element according to the invention is comprised of hot-rolled, austenitic manganese steel that has no edge carbide layer and that becomes very hard when cool-shaped. According to the method, the hot rolled-edge carbide layer is trimmed off both sides, or the formation of this layer is avoided by the use of a protective gas.
U.S. Pat. No. 5,458,704 describes a hot-rolled armor steel that contains by weight
0.25 to 0.32%carbon,0.05 to 0.75%silicon,0.10 to 1.50%manganese,0.90 to 2.00%chromium,0.10 to 0.70%molybdenum,1.20 to 4.50%nickel,0.01 to 0.08%aluminum,max. 0.015%phosphorous,max. 0.005%sulfur,max. 0.012%nitrogen, andbalance iron and smelting impurities.This steel is provided for armor with a wall thickness of at is least 50 mm.
German 200 14 361 describes a one-piece hot-shaped B-column with a very strong upper part and a relatively ductile lower part in its construction, where parts of the lower part are insulated in the oven to prevent austenitizing, or before hardening, are cooled without reaching the critical temperature.
German 697 07 066 describes a hot-shaped B-column with a special hardness distribution that extends arcuately so when cooled the highest hardness level is in the middle of the B-column.